Key facts about LED backlights

12/10/2012 in category "Science"2036

One of the major and defining monitor technology trends of recent times has got to be the push of affordable and efficient LED (Light Emitting Diode) backlights. Although this technology surfaced a number of years ago it has been gathering increasing traction. With many manufacturers such as Samsung, BenQ and ViewSonic focussing their current efforts almost exclusively on promoting this ‘green’ form of backlighting it is easy to get lost in the forest of hype. Like most things to do with monitor technology and indeed technology more broadly the marketing machine often puts an awful lot of spin on emerging technologies such as LED backlighting. With huge and misleading contrast claims and the tendency to forgo the word ‘backlight’ entirely – as if this is some technology distinct from ‘LCD’ monitors – it understandably creates considerable confusion. This article aims to dispel some of the misconceptions and confusion that shrouds the technology by looking at the real advantages and the potential drawbacks of monitors using LED backlights.

The advantages:

Monitors with LED backlights are widely available. They have seen significant market growth recently and is now included in various panel types; IPS, VA and TN – all of these are types of LCD panel!

An ‘edge backlight’ arrangement using white LEDs (WLED) is by far the most common, especially on consumer models. This is a simple and relatively cheap implementation that places a border of white LEDs around or just behind the LCD panel.

These LEDs can be activated at full brightness almost instantly, allowing very high dynamic contrast ratios to be achieved. The image does not undergo significant changes as the diodes ‘warm up’, unlike ‘traditional LCDs’ using CCFLs (Cold Cathode Fluorescent Lamps).

WLED is very energy efficient, allowing the monitor to offer a power saving of 30-40% or more over an equivalent CCFL model. They also produce less heat as a result which really makes a difference if you have an office full of screens or are using the monitor in a small room at home.

Unlike CCFL bulbs, LEDs do not contain mercury and can be recycled more easily.

The LED backlight can be made very thin to create monitors that are relatively thin and light. Some consumers find this an attractive and somewhat fascinating aspect of the technology. Some models are literally ‘finger thin’.

The disadvantages:

This is more of a neutral point than a disadvantage but is worth paying attention to. The whole backlight is controlled as one Backlight Unit (BLU) on modern LED designs meaning that you can only brighten or dim the entire screen at the same time. There is therefore no static contrast advantage (the more useful measure of contrast) over CCFL designs.

Thin monitors may look striking but they are more prone to post-manufacturing stress and flexation. This can increase the extent or likelihood of ‘backlight bleed’ that is particularly noticeable when viewing dark content in a dark room. There are no guarantees with this regardless of the display’s thickness, though, and there were plenty of problematic CCFL backlit models in this regard.

Many LED backlights use PWM (Pulse Width Modulation) to dim to below 100% brightness. This involves a very rapid ‘on-off’ cycle which some users are sensitive to, detecting flickering which they may find bothersome.

The vast majority of WLED backlights are restricted to ‘standard gamut’, often around 72% NTSC (100% sRGB) but sometimes extending slightly beyond this. This is far lower than some CCFL designs that have been around for years which extend to beyond NTSC and fully covering AdobeRGB. There are some improved WLEDs in development which cover the AdobeRGB colour space but it may be some time before this is widely availability.

Conclusion:

There are some definite advantages to ‘LED monitors’, mainly in terms of energy efficiency and stylish design. But they still use LCD technology and are not some new-fangled thing which will revolutionise image quality in the way manufacturers may lead you to believe. There are also some disadvantages to the technology, such as restrictions to colour space, less sturdy screens and potential ‘PWM’ flickering which some users may find disturbing. Some recent and upcoming developments by big panel manufacturers such as LG and Samsung are starting to neutralise these disadvantages, providing extended colour spaces and forgoing PWM dimming of the backlight. Either way there is no question that LED technology is here to stay and that it is a change that is largely positive for the consumer.

Author Bio. Adam Simmons is a display enthusiast who shares his knowledge on pcmonitors.info